The processing and disposal of wastewater treatment sludge are increasingly important topics of environmental, economical and technological concern. Recently, the waste volumes produced have increased dramatically as a result of increases in the organic loading of wastewater and environmental regulations that require a higher degree of wastewater treatment. After sewage treatment at wastewater plants there is still over 1 million ton sludge produced each year in Sweden. By tradition, this sludge has been spread out on fields as fertilizer, or it has been deposited or combusted. However, many problems have arisen. In 1999 Lantbrukarnas Riksförbund, the farmer's national union in Sweden, warned their members from using sludge as fertilizer as they suspected the sludge to contain hazardous substances. Disposal by land filling is also becoming increasingly expensive. The growing and closing of landfills, public concerns over ground-water contamination and safety problems associated with methane production as a result of biological activity in landfills further expand the problem. Public concern over possible hazardous products through combustion processes such as dioxins and possible heavy metal contamination from the resulting ash is also problematic. Therefore a new waste tax was introduced in January 2002 to encourage researchers to find a better solution. By year 2005, the situation becomes even more critical as by then it will be completely illegal to deposit organic material as sludge. Therefore, the problem with the great amount of sludge mass is urgent today.
Certain wastewater treatment methods comprise biological techniques, such as aerobic treatment, anaerobic treatment, and other anoxic processes (denitrification, sulphate reduction). The biological techniques clearly have the greatest potential for treating wastewater. Biological processes can be used to remove and/or recover biodegradable organic compounds, nitrogen, phosphorus and sulphuric compounds, pathogenic organisms and various heavy metals.
Biological processes are used extensively in the treatment of domestic and industrial wastewater. The quality of the effluent water depends on effective removal of the pollutants by metabolic activity of the aerobic microorganisms. The activity depends on the growth rate which is regulated by the dissolved oxygen and medium composition. Aerobic conditions are favouring oxidation of substances responsible for the unpleasant odour of fermented sludge.
Oxygen solubility has always been an important issue in many aerobic fermentation processes, because oxygen unlike other nutrients is sparingly soluble in aqueous media. The mass transfer rate of oxygen from oxygen rich phase to media is often a rate limiting factor in the processes. Therefore oxygen has to be continuously supplied to media to meet the oxygen demand required for actively respiring cells to do the metabolism which will not be effected by the lack of oxygen. Shortage of dissolved oxygen is hampering the biological digestion of sludge and oxidation reaction e.g. nitrification and detoxication of wastewater. Bioremediation of hazardous toxicants such as dioxins and pesticides is oxygen dependant.
Today the lack of oxygen in the biological purification steps is partially solved by supplying oxygen by pumping to these biological steps. This requires a high energy supply which is expensive. However, since there still remains a considerable amount of sludge, which must be deposited and discarded, new means for supplying oxygen to the biological steps are required, so that a more effective digestion is accomplished.
In WO86/03773 there is described a process for increasing the solubility of gases in an aqueous medium and an emulsion for carrying out said process. Said emulsion comprises a copolymer of a silicone and a hydrophilic compound.
Due to the restricted laws regarding disposal of organic material as sludge in the coming years there are urgent needs to develop new means to digest sludge more efficiently. The present invention provides a solution to the above mentioned problem.